Recently, with the development of electronic industries and the advance of industrial technologies, various electronic devices are designed toward small size, light weightiness and easy portability. Consequently, these electronic devices can be applied to mobile business, entertainment or leisure purposes whenever or wherever the users are. For example, various camera modules are widely used in many kinds of fields such as smart phones, wearable electronic devices or any other appropriate portable electronic devices. Since the electronic devices are small and portable, the users can take the electronic devices to capture images and store the images according to the users' requirements. Alternatively, the images can be uploaded to the internet through mobile networks. In other words, these electronic devices not only have important commercial values but also provide more colorful lives to people. In addition to the applications on the portable electronic devices, most camera modules are applied to the vehicular electronic devices in order to meet the high safety requirements.
FIG. 1 schematically illustrates the concepts of a conventional camera module. The camera module 1 comprises a camera lens 11 and a photosensitive element 12. After an ambient light beam passes through the camera lens 11, the ambient light beam is projected on the photosensitive element 12. Consequently, an image is acquired. For increasing the imaging quality of the camera module 1, it is important to align an optical axis 111 of the camera lens 11 with an imaging center 121 of the photosensitive element 12. Consequently, during the process of fabricating and assembling the camera module 1, it is important to effectively test whether the optical axis 111 of the camera lens 11 is aligned with the imaging center 121 of the photosensitive element 12.